The nucleosome, composed of an octamer of highly conserved histone proteins and associated DNA, is the fundamental unit of eukaryotic chromatin. How arrays of nucleosomes are folded into higher-order structures, and how the dynamics of such compaction is regulated, are questions that remain largely unanswered. This proposal seeks to understand the role of core histone phosphorylation in regulating higher-order chromatin structure and altering epigenetic landscapes. More specifically, histone phosphorylation will be studied in the context of mitosis, apoptosis and DNA damage. One long-range objective of this proposal is to better understand the role that core histone phosphorylation plays in mediating cis versus trans mechanisms with an emphasis on effectors (readers) that engage phosphorylation modifications in a context-dependent fashion. A second long-range goal of this research program is to determine the enzyme systems responsible for adding (kinases or writers) or subtracting (phosphatases or erasers) these phosphorylation marks. We hypothesize that histone phosphorylation acts as molecular switches, or as part of potentially redundant, modification cassettes to govern critical downstream chromatin associations with key effectors to determine compaction states. Understanding the physiological substrates and sites phosphorylated by these enzymes is of paramount importance. Just as studies on histone acetylation and methylation have led to a wealth of new insights into mechanisms of transcription, we anticipate that insights into histone phosphorylation will pave the way for a better understanding of chromosome condensation and DNA repair. To achieve these goals, we will employ complementary genetic, biochemical and immunocytochemical approaches in a variety of model systems. The highly conserved nature of histone proteins, as well as the phosphorylation events and the relevant enzyme systems involved, underscore the fundamental nature of the chromatin problem for all DNA-templated processes. The close association of histone kinases, such as aurora kinase, and specialized histone variants, such as H2A.X, with oncogenesis provides strong support for an emerging view that covalent modifications of histones plays a vital role in the regulation of chromatin dynamics with far-reaching implications for human biology and disease, notably cancer.